Sheet hold down and uncurler

ABSTRACT

Sheet conveying apparatus including a power-driven support for supporting one face of a sheet and carrying the sheet along a path in the direction of one of its edges. An overlying hold-down for the sheet includes an elongate, endless, flexible band trained over sheaves which provide an elongate reach of the band extending parallel to the support surface and in the direction of the path. The hold-down band is driven at substantially the same speed as the support. The sheaves training the hold-down band adjacent its upstream and downstream ends are mounted for movement toward and away from the underlying support independently of each other. An uncurling device at the upstream end of the hold-down apparatus is operable to remove a curl from the leading edge of a sheet supplied to the apparatus. The uncurling device includes an elongate, endless, flexible band trained over a pair of spaced sheaves, to provide a reach for the uncurling band which inclines outwardly from the support surface on progressing in an upstream direction from the upstream end of the reach of the hold-down band. The uncurling band is driven at a faster speed than the hold-down band and conveyor support to remove the curl from the leading edge of a sheet.

United States Patent [191 Fritz Sept. 23, 1975 SHEET HOLD DOWN AND UNCURLER Dennis W. Fritz, Lake Oswego, Oreg.

[75] Inventor:

[73] Assignee: Amos A. Homer, Cascadia, Oreg. a

part interest [22] Filed: Feb. 1, 1974 [21] Appl. No.: 438,522

Primary ExaminerRichard A. Schacher Attorney, Agent, or FirmKolisch, Hartwell, Dickinson & Stuart [57] ABSTRACT Sheet conveying apparatus including a power-driven support for supporting one face of a sheet and carrying the sheet along a path in the direction of one of its edges. An overlying hold-down for the sheet includes an elongate, endless, flexible band trained over sheaves which provide an elongate reach of the band extending parallel to the support surface and in the direction of the path. The hold-down band is driven at substantially the same speed as the support. The sheaves training the hold-down band adjacent its upstream and downstream ends are mounted for movement toward and away from the underlying support independently of each other. An uncurling device at the upstream end of the hold-down apparatus is operable to remove a curl from the leading edge of a sheet supplied to the apparatus. The uncurling device includes an elongate, endless, flexible band trained over a pair of spaced sheaves, to provide a reach for the uncurling band which inclines outwardly from the support surface on progressing in an upstream direction from the upstream end of the reach of the hold-down band. The uncurling band is driven at a faster speed than the hold-down band and conveyor support to remove the curl from the leading edge of a sheet.

18 Claims, 6 Drawing Figures SHEET HOLD DOWN AND UNCURLER BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to sheet conveying apparatus 5 including hold-down means for maintaining the sheet in a desired configuration as it is conveyed along a path, and more specifically, to said apparatus which includes means adjacent its infeed end for removing a curl which may exist at theleading edge of the sheet as it is fed to the apparatus.

In the conveying of material, such as sheets of veneer, it often is necessary to convey them along a path with the same held in a substantially planar configuration. Such is the case where a sheet is to be conveyed over a scanning device for detecting flaws in the sheets to provide actuating control for a clipper or other apparatus. Apparatus for holding the sheet in a desired position as it is conveyed through the apparatus should be so constructed that the chance for damage to the sheet occurring is minimized. Such apparatus also should be adapted to receive and operate upon sheets of various thicknesses, or varying numbers of sheets in stacks carried therethrough.

Sheet material, and particularly sheets of veneer which are peeled from logs, often are supplied to conveying apparatus with the leading edge thereof curled. Such a curl is produced by the action of a cutting knife which peels veneer from a rotated log. It is therefore necessary in apparatus for dealing with such sheets, to provide some means for removing the curl from the leading edge of such sheets prior to feeding it between a pair of opposed members. Should the sheet be carried into the region between opposed members with the curl remaining in its forward edge, a crease may be formed in the material, or .it may be broken.

A general object of the present invention, therefore, is to provide sheet conveying apparatus including novel hold-down means for holding a sheet of material conveyed through the apparatus against a moving sheet support, which hold-down apparatus is relatively simple and inexpensive in construction.

Another object is to provide such novel hold-down apparatus which includes an elongate, endless, flexible member trained over spaced wheels to produce a reach of the member extending generally in the direction of the path. The training members are mounted for movement independently of each other toward and away from the sheet support and are yieldably biased toward the support permitting holding of various thicknesses of sheets or multiple sheets in a stack without loss of efficiency or damage occurring to the sheets.

Still another object is to provide sheet conveying apparatus which includes novel uncurling apparatus adjacent the infeed end thereof operable to remove a major portion of the curl which may exist at the leading edge of a sheet fed to' the apparatus prior to such being carried into a position between opposed sheet-holding members.

A further object is to provide such apparatus including an uncurler in which the uncurler includes an elongate, endless, flexible band trained about a pair of sheaves spaced apart generally in the direction of movement of a sheet carried through the apparatus, to provide an uncurling reach for the band. The downstream end of the uncurling reach of the band is relatively closely spaced to an opposed sheet carrying conveyor, and remainder portions of the uncurling reach incline outwardly therefrom on progressing in an upstream direction. The uncurling band is driven at a faster speed than is the conveyor support surface so that the curved leading edge of a sheet will be engaged by the uncurler band and driven forwardly of remainder portions thereof carried on the underlying conveyor support surface, thus to provide an uncurling action for the leading edge of the sheet.

Yet another object is to provide such novel holddown apparatus in which the hold-down member is an elongate, endless, flexible band and one of the training members is a sheave having a relatively shallow V- shaped groove therein which maintains the band substantially centered in the sheave, yet which permits foreign'material, such as splinters which may be found in the carrying of veneer, to pass between the sheave and band and be ejected therefrom, without causing the band to be unseated from the sheave. Thus, maintenance and damage to the system is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages will become more fully apparent as the following description is read in conjunction with the drawings, wherein:

FIG. 1 is a perspective view of sheet conveying apparatus including a hold-down and uncurling device constructed in accordance with an embodiment of the invention; I

FIG. 2 is a top plan view of such a hold-down and uncurling device on a larger scale than shown in FIG. 1;

FIG. 3 is a side elevation view of the hold-down and uncurling device shown in FIG. 2;

FIG. 4 is a cross-sectional view, on an enlarged scale, taken generally along the line 4-4 in FIG. 3;

FIG. 5 is a cross-sectional view, on an enlarged scale, taken generally along the line 5-5 in FIG. 3; and

FIG. 6 is an enlarged view taken generally along the line 66 in FIG. 3.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Referring to the drawings, and first more specifically to FIG. 1, at 10 is indicated generally conveyor apparatus operable to carry material, such as sheets of veneer, in a substantially horizontal position along a path in the direction of arrow 12, to the left in FIGS. 1 and 2. Apparatus 10 includes a substantially planar table 14 over the top of which the upper, elongate, substantially parallel reaches of a plurality of power-driven conveyor belts 18 run. 1

The conveyor belts are operatively connected, through appropriate sprockets and drive chains 16, to an output shaft of a gear box 17. The input shaft of gear box 17 is operatively connected to the output shaft of a reversible, variable speed motor 20, whereby operation of the motor in one direction produces movement of the upper reaches of belts 18 to the left in FIGS. 1 and 3. Operation of the motor in a reverse direction moves the upper reaches of the belts in a reverse direction, to the right in FIGS. 1 and 3. The conveyor belts are operable to receive sheet material thereon, such as a sheet of veneer, support one face of the sheet, and on being driven in the direction of arrow 12 carry the sheet in the direction of one of its edges along a path over table 14..

Referring to FIGS. 1 and 3, at 22 is indicated generally an elongate clipper blade shiftable toward and away from an underlying anvil 24 to clip portions from sheets of veneer carried therebetween.

An elongate scanning element 26 extends across table 14 intermediate upstream and downstream reaches of conveyor belts l8. Scanner 26 is operable to detect selected characteristics of sheets of veneer carried thereover and is interconnected through appropriate control mechanism to operating means for clipper 22 in such a manner as to actuate the clipper to cut the sheets of veneer as required as sensed by the scanner. Such a scanner generally requires that a sheet of veneer be held rather closely thereover.

A plurality of sheet hold-down devices, indicated generally at 30, are mounted over table 14 with each such device overlying a conveyor belt 18 and scanner 26. Each hold-down device is operable, as will be described in greater detail below, to hold a sheet in a substantially planar configuration atop table 14 and scanner 26 as it is carried by belts l8.

Describing a hold-down device 30, an elongate, substantially horizontal shaft 32 spaced a distance above the upper reaches of conveyor belts 18 extends transversely of the conveyors. Shaft 32 is journaled for rotation adjacent its opposite ends through pillow blocks such as that indicated generally at 34. A sprocket 36 secured to an end of shaft 32 is operatively connected through a drive chain 38 to another output shaft of gear box 17 which rotates in a direction opposite the direction of rotation of the output shaft to which chain 16 is connected. Shaft 32 thus is drivingly connected through gear box 17 to motor 20 also and the powerdriven portions of hold-down devices 30 will be driven in timed relationship with the movement of underlying conveyor belts 18, as will be described in greater detail below.

Referring to FIGS. 2 and 3, a hold-down device 30 includes a drive sheave 40 which is secured to shaft 32 for rotation therewith.

Extending rearwardly, or in an upstream direction relative to the conveyors, to the right in FIGS. 2 and 3, from shaft 32 are a pair of laterally spaced elongate support rods 44, 46. One set of ends of support rods 44, 46 are connected through journal connectors 50, 52, respectively, to shaft 32 for pivotal swinging independently of rotation of shaft 32 toward and away from underlying conveyor belts 18.

A pair of elongate, guide sleeves 54, 56 are slidably mounted on the opposite set of ends of rods 44, 46, respectively. Support plates, such as that indicated generally at 60 are secured to and dependently supported on sleeves 54, 56. Collars 62 are secured on rods 44, 46 intermediate their ends. A pair of elongate compression springs 64 interposed between collars 62 and sleeves 54, 56 yieldably bias sleeves 54, 56 away from shaft 32.

A sheave 68 is journaled between plates 60 for rotation about an axis extending substantially parallel to shaft 32. As is best seen sheave 68 is disposed substantially in line with sheave 40. Another sheave 69, disposed to one side of sheave 68, also is journaled between plates 60 for rotation independently of sheave 68. Sheave 69 is smaller in diameter than sheave 68.

A pair of elongate, laterally spaced, substantially parallel support arms 70 are secured to plates 60 on sleeves 54, 56 and project rearwardly therefrom. Arms incline upwardly and away from underlying conveyors 18 on progressing in an upstream direction in the apparatus.

Adjacent the outer, or upstream, set of ends of support arms 70 are journaled a pair of side-by-side sheaves 74, 76. As is best seen in FIG. 2, sheave 74 is disposed substantially in line with sheaves 68, 40, and sheave 76 is disposed substantially in line with sheave 69. Sheave 76 is considerably larger in diameter than sheave 74. These two sheaves are keyed together for rotation as one.

Extending forwardly, in a downstream direction relative to the path of movement of conveyors 18, from shaft 32 are a pair of laterally spaced, elongate support bars 80, 82. Bars 80, 82 are pivotally connected at one set of their ends to shaft 32 through a pair of journal connections 86 disposed on opposite sides of sheave 40. Such journal connections permit swinging of bars 80, 82 vertically, toward and away from conveyors 18, independently of rotation of shaft 32.

A pair of support blocks 88, 90 are secured to and depend from support bars 80, 82, respectively. Journaled for rotation intermediate blocks 88, 90 is an idler sheave 92 disposed substantially in line with drive sheave 40.

Secured to and projecting in a downstream direction from the downstream set of ends of arms 80, 82 are a pair of laterally spaced, substantially parallel support plates 94, 96. Extending between and journaled adjacent its opposite ends on plates 94, 96 is a sheave 100. The configuration of sheave 100 is best illustrated in FIG. 4 wherein it can be seen that it has a relatively shallow V-shaped peripheral configuration.

An elongate, endless, flexible hold-down band, or member, indicated generally at 104, is trained over sheaves 40, 74, 68, 100 and 90 as shown in FIG. 3. Band 104 may have a substantially circular cross section as indicated in the cross-sectional view in FIG. 4 and may be made of a urethane plastic.

Sheave 100, as is best seen in FIG. 4, has an end-toend dimension which is greater than three times the diameter of band 104. The opposite, outer ends of sheave 100 have substantially similar diameters and are considered the major diameter portions of the sheave. The minor diameter of the sheave is disposed substantially centrally between its opposed outer ends. The difference between the radius of an outer end of the sheave and the radius at the center of the sheave is less than the diameter of band 104. A side portion of band 104 thus projects outwardly beyond the peripheral edges of sheave 100. A shallow central groove 106 extending circumferentially about the central region of sheave I00 aids in maintaining band 104 in a centered position on the sheave. With such a sheave, when band 104 is driven therearound, the band will naturally seek the center of the sheave and be retained generally in the center thereof.

As is best seen in FIG. 3, with band 104 trained about the sheaves as illustrated, a portion of the band extending between sheaves 68, 100 extends in a substantially horizontal reach 104a which overlies and is substantially parallel to the upper reaches of conveyor belts 18. This is referred to herein as the hold-down reach of the band.

Referring to FIGS. 2, 3, 4 and 5, an elongate deflector block 110 is secured between the downstream ends of support bars 80, 82. The block is positioned in the apparatus in such a manner that when support bars 80, 82 are in the position shown in FIG. 3, the underside of block 110 is disposed substantially horizontal and parallel to the upper reach of an underlying belt 18. The underside of block 110 may have an elongate groove, such as is indicated at 112, extending therealong through which a portion of lower reach 104a of band 104 may travel. The upstream end of block 110 is shaped to provide a pair of angularly disposed deflector surfaces 113, 114 facing generally in an upstream direction in the apparatus. The block functions to deflect debris, such as splinters or other material, which maybe carried by band 104, or a sheet conveyed through the system, thus to inhibit such debris from entering the nip between band 104 and sheave 100.

Another elongate, endless, flexible band 1 16, also referred to herein as an uncurling member, is trained over sheaves 69, 76. Band 116 also may be made of urethane material and has a substantially circular cross section, as previously described for band 104. The lower reach 116a of band 116, extending between the lower peripheral edges of sheaves 69, 76, inclines upwardly, or outwardly, from belt 18 on progressing in an upstream direction in the apparatus from sheave 69. Band 1 16 and the support and drive means therefor are referred to collectively herein as straightening means. Referring to FIGS. 3 and 6, pivotally connected to and depending from support plates 60 is a band reverse guide 120. Reverse guide 120 includes a pair of laterally spaced elongate bars 122 which are pivotally connected adjacent their upper set of ends to a rod 124 extending between plates 60. Bars 122 are spaced apart by a spacer rod 126 adjacent their lower set of ends a distance slightly greater than the diameter of band 104. Bars 122 are maintained in a position substantially aligned in an upstream to downstream direction with sheave 68. Bars 122 are swingable in a substantially downstream direction about rod 124 from the substantially vertical position shown in FIG. 3, but are prevented from swinging in an upstream direction by a rod 128 extending between and secured to side plates 60. Lower end portions of bars 122 straddle opposite sides of reach 104a of band 104 and serve to guide this lower reach of the band when run in a reverse direction, as will be explained more fully below.

Referring to FIGS. 1, 2 and 3, secured to support plate 94 adjacent the downstream end of the holddown device is an upright lifting arm 132. An elongate cable 134 is secured at one of its ends to arm 132 and extends upwardly therefrom to be secured at its upper end to an elongate, rotatable shaft 136 extending transversely of and above the downstream end of the conveyor and hold-down devices. Rotation of shaft 136 in a clockwise direction as viewed in FIG. 3 wraps cable 134 thereabout to raise the downstream ends of support bars 80, 82 and the hold-down mechanism supported thereon, while counterclockwise rotation of shaft 136 lowers cable 134 and the downstream ends of the bars and mechanism supported thereon to the position shown in FIG. 3 resting atop the conveyors.

Describing now the operation of the apparatus, a sheet of veneer may be fed to the apparatus and supported with one of its faces resting on the upper reaches of belts 18. On operation of motor in one direction the upper reaches of belts 18 are moved in a downstream direction, to the left in FIGS. 1 and 3. The veneer sheet supported on the belts is conveyed in a downstream direction therealong, to the left in FIGS. 1 and 3. As is best seen in FIG. 3, the leading edge of such a sheet of veneer, indicated generally at 140, may be curled upwardly from underlying support belts 18.

As belts 18 are driven to carry such a sheet of veneer toward scanner 26 and clipper 22, shaft 32 and drive sheaves 40 of the hold-down devices are driven in clockwise directions as seen in FIG. 3. This produces movement of band 104 over its support sheaves, whereby its lower reach 104a travels in a downstream direction parallel to the direction of travel of the upper reaches of belts 18. The driving connection between conveyors 18 and band 104 is such that lower reach 1040 of band 104 travels at substantially the same speed-as the upper reaches of belts 18.

Since sheaves 74, 76 are keyed together to rotate as one, driving of belt 104 results in a corresponding driving of band 116. It should be recognized that since sheave 76 over which band 116 is trained is considerably larger than sheave 74 around which band 104 is trained, reach 116a of band 116 will travel in a downstream direction at a much faster speed than does the lower reach 104a of belt 104. Reach 1 16a thus is driven in a downstream direction at a speed which is a preselected multiple of the speed of belts 18 and band 104. Should the speed of belts 18 and band 104 change, a corresponding change in the speed of band 116 will occur.

With such apparatus, sheet 140 is carried at the speed of conveyor belts 18 on which it is supported. As it is moved downstream along the conveyors its curled leading edge is contacted by the lower reach 116a of band 116 which causes the curled leading edge of the veneer sheet to travel at a faster speed than remainder portions supported on belt 18. This acts to uncurl the sheet as illustrated in the sequential dot-dashed positions illustrated at 104a-140d. The leading edge of the sheet should be sufficiently flattened, whereby it will run smoothly into the nip between belt 18 and band 104 in the region where band 104 is trained over sheave 68.

It should be recognized that since sheave 69 is smaller in diameter than sheave 68 the lowermost portion of band 116 where it travels under sheave 69 is spaced a distance above belt 18. This permits band 1 16 to release its force on the veneer sheet as the sheet is engaged by band 104 for holding it down as it is carried along the conveyor.

As the sheet is carried under the hold-down devices the weight of the sheaves and support means for the sheaves yieldably bias the sheaves and reach 104a of band 104 toward belts 18 to hold the sheet in a substantially planar configuration against the upper reaches of conveyor belts 18.

With the upstream and downstream sheaves 68,

which train band 104 to form reach 104a being freely pivotal about shaft 32 they may raise and lower independently of each other to accommodate variations in thickness of material conveyed thereunder. For example, various thicknesses of veneer sheets may be accommodated by the apparatus and still maintain a holddown force thereon, or, if desired, stacks of sheets may be conveyed thereunder with such hold-down device accommodating stacks up to a thickness equal to the space between reach 104a and the underside of drive sheave 40.

Should material become clogged in the apparatus adjacent clipper 22 the forwardmost, or downstream, end of the hold-down device may be raised by clockwise rotation of shaft 136 as seen in FIG. 3 to raise belt 104 and its supporting mechanism to allow removal of material fr'om thereunder.

With the drive means for conveyors 18 and band 104 being reversible the belts and bands may be driven in an upstream direction to remove clogs of material therefrom, or for other desired reasons. When band 104a is driven in a reverse'direction, reverse guide 120 aligned with sheave 68 serves to prevent reach 104a of the band from jumping out of sheave 68.

As has been mentioned previously, block 110 adjacent sheave 100 is operable to deflect debris carried by a veneer sheet and band 104 from a path which might carry it into the nip between band 104 and sheave 100. However, should debris, such as splinters or other material, be carried into the nip between the band and sheave 100 the shallow V-shaped configuration of sheave 100 serves to aid in preventing the band from being forced out of the sheave. Explaining further, should a splinter of wood be caught between sheave 100 and band 104, it may ride up and over the sheave with the band and then be dropped on the back side of the sheave without unseating the band from the sheave. The configuration of the sheave allows the band to shift laterally somewhat and still remain on the sheave, and after the foreign material has been dropped therefrom the band naturally seeks the center of the sheave again.

Thus, it will be seen that a very useful and adaptable hold-down device for sheet material is provided by the instant invention. Further, the uncurling mechanism at the upstream end of the hold-down device provides means for removing a curl from the leading edge of a sheet of veneer carried along a conveyor prior to its being fed to the region between the conveyor and the hold-down band. This prevents clogging of the apparatus and breakage of veneer sheets which has been a problem in the past.

By use of urethane bands, good traction on the material is provided for carrying it through the device reducing skewing due to slippage or uneven flow in the-apparatus. By use of a urethane band, there is little, if any, chance of damage occurring to the surface of veneer carried thereunder. The spring loading of the support for the rearmost sheaves assures a constant, even tension in band 104 regardless of the positioning of the sheaves relative to each other caused by raising or lowering of the upstream and downstream sheaves relative to each other.

While a preferred embodiment of the invention has been described herein, it should be apparent to those skilled in the art that variations and modifications are possible without departing from the spirit of the invention.

It is claimed and desired to secure by letters patent:

l. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprisan elongate, endless, flexible hold-down member,

a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said holddown member being trained around said training members to provide an elongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member being positioned to contact the face of a sheet opposite its face supported by said support means,

means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said training members toward said support means, and

means for driving said reach of the holddown member in said one direction including a rotatable drive member over which said hold-down member is trained, which drive member is disposed between said pair of training members and is spaced outwardly from said reach of the hold-down member in a direction away from said path.

2. The device of claim 1, wherein said drive means comprises an elongate, power-driven rotatable shaft spaced outwardly from and extending transversely of said path, said drive member is secured on said shaft for rotation therewith, and said means mounting a training member comprises an elongate support extending generally in the direction of said path pivotally mounted adjacent one of its ends on said shaft for swinging movement independent of rotation of said shaft toward and away from said support means and said training member is journaled on said support adjacent its opposite end.

3. The device of claim 1, wherein said means mounting said training members comprises a first elongate support pivotally mounted adjacent one of its ends adjacent said drive member and extending in a generally downstream direction therefrom relative to said path with one of said training members journaled on said first support adjacent its other end, and a second elongate support pivotally mounted adjacent one of its ends adjacent said drive member and extending in a generally upstream direction therefrom relative to said path with the other of said training members journaled on said second support adjacent its opposite end, said first and second supports being swingable toward and away from said support means independently of each other.

4. The device of claim 3, wherein one of said supports comprises means mounting its associated training member for shifting toward and away from the other of said training members generally in the direction of said path and means yieldably biasing said training member away from said other training member to maintain tension in said reach of the hold-down member.

5. The device of claim 1, wherein said hold-down member comprises an elongate, flexible band having a substantially circular cross section, and one of said training members comprises a sheave having a width which is at least three times the diameter of said band and wherein the difference between the minor radius and the major radius of the sheave is less than the diameter of said band.

6. The device of claim 5, wherein the opposite ends of said sheave have substantially the same diameter, the minor diameter of the sheave is disposed substantially centrally of said outer ends, and the surfaces of the sheave extending from said outer ends toward said minor diameter region are inclined at a substantially constant shallow angle relative to the rotational axis of the sheave.

7. The device of claim 6, wherein said sheave has a shallow groove extending circumferentially thereabout' in said minor diameter region.

8. A sheet hold-down device for use with conveying apparatus including a support means for supporting one face of a sheet as it is moved along a path in the direction of one ofits edges, said hold-down device comprising, 4 l

an elongate, endless, flexible hold-down member,

a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said holddown member being trained around said training members to provide an elongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member being positioned to contact the face of a sheet opposite its face supported by said support means,

means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said training members toward said support means,

means for driving said reach of the hold-down member in said one direction, and

a deflector mounted intermediate said training members and closely adjacent the training member which is positioned farthest downstream in said apparatus relative to the direction of movement of said path, said deflector having a notch in its side facing toward the sheet support means adapted to receive and permit travel of a portion of said holddown member thereunder.

9. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one ofits edges, said hold-down device comprising,

an elongate, endless, flexible hold-down band,

a pair of training sheaves journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said hold-down band being trained about said training sheaves to provide an elongate reach extending in said direction adjacent and substantially parallel to said support, said reach of the hold-down band being positioned to contact the face of a sheet opposite its face supported by said support means,

means mounting said training sheaves for shifting toward and away from said support means independently of each other and yieldably biasing said training sheaves toward said support means,

reversible drive means for driving said reach of the hold-down band in said one direction or in a direction opposite said one direction, and

a band guide pivotally mounted above said reach of the band intermediate said sheaves and closely adjacent said sheave toward which said reach of the band moves on being driven in said opposite direction, said guide having depending, laterally spaced, side portions extending downwardly on opposite sides of said reach of the band defining a guide channel therebetween which is substantially aligned with a band-receiving peripheral groove of the sheave near which it is mounted.

10; The device of claim 9, wherein said guide is mounted for swinging-upwardly and away from said band when the band is driven in said one direction and is retained in a guiding position with its depending side portions guiding movement of said reach when said reach is moved in said opposite direction.

11. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprising? an elongate, endless, flexiblehold -down member,

a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement fora sheet, said holddown member being trained around said training members to provide anelongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member U being positioned to 'contact the face of a sheet opposite its face supported by said support means, withthe training member of said pair which is positioned farthest upstream relative to said path training said hold-down member in a bend whereby a sheet catching nip is defined between the holddown-member and the support means,

means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said linetraining members toward said support means,

means for driving said reach of the hold-down member in said one direction, and

straightening means for removing a curl from the leading edge of a sheet prior to such leading edge reaching said sheet catching nip, said straightening means comprising an elongate, endless, flexible uncurling member, means training said uncurling member thereover to provide an elongate uncurling reach for the uncurling member extending 'in a generally upstream direction relative to said path from a region'adjacent said nip, with said uncurling reach diverging from said support means on progressing in said upstream direction, and means for driving said uncurling reach in the direction of said path at a speed faster than the speed at which a sheet is carried along said path.

12. The device of claim 11, wherein the speed at which said hold-down member is driven corresponds to the speed at which a sheet is carried along said path by the conveyor, and which further comprises means operatively interconnecting said hold down means and said straightening means operable to drive said uncurling member at a speed which is preselected multiple of the speed of said hold-down member regardless of variations in the speed of the hold-down member.

13. The device of claim 11, wherein said training means for said uncurling member comprises a wheel around which said uncurling member is trained, said wheel being journaled adjacent the upstream training member for the hold-down member and being so positioned that the portion of the uncurling member nearest said support means is spaced from said support means a distance greater than is said hold-down member at the nip between the hold-down member and the support means.

14. Sheet-conveying apparatus for conveying a sheet along a path in the direction of one of its edges wherein the leading edge of such a sheet may be curled when supplied to the apparatus, comprising sheet-support means having a support surface for supporting one face of a sheet, and being movable at a first speed in the direction of said path to carry a sheet therealong,

hold-down means including a power-driven, elongate hold-down member having an elongate reach extending substantially parallel to and overlying said sheet support means, with a portion of said member adjacent the upstream end of said reach converging toward said sheet support means to provide a sheet catching nip therebetween, said reach being movable at substantially the same speed as said sheet support means, and

straightening means for removing a curl from the leading edge of a sheet carried by said support means including an elongate, endless, flexible uncurling member, means training said uncurling member to provide an elongate uncurling reach thereof extending generally in the direction of said path, with an upstream portion of said uncurling reach being spaced a distance upstream along said path from said sheet catching nip and spaced a distance outwardly from said support surface and with remainder portions of said uncurling reach extending from said upstream portion to a region adjacent said sheet catching nip and converging toward said support surface on progressing in a downstream direction relative to said path, and drive means for driving said uncurling reach at a speed faster than the speed of movement of said support means.

15. The apparatus of claim 14, wherein said flexible uncurling member is an endless band and said training means comprises a pair of sheaves journaled for rotation about substantially parallel axes extending transversely of said path, with the sheave which is positioned downstream in said pair relative to said path being mounted with its peripheral edge nearer to said support means than the other of said sheaves.

16. The apparatus of claim 14, wherein said sheet support means comprises variable speed drive means operable to move the sheet support means at selected speeds, and said uncurling means is operatively connected thereto through means operable to drive said uncurling reach at a speed which is a preselected multiple of the speed of the sheet support regardless of the speed of the support means.

17. Sheet-conveying apparatus for conveying a sheet along a path in the direction of one of its edges wherein the leading edge of such a sheet may be curled when supplied to the apparatus, comprising sheet-support means having a support surface for supporting one face of a sheet, and being movable at a first speed in the direction of said path to carry a sheet therealong,

hold-down means including a power-driven, elongate, endless, flexible band, and means training said band in a hold-down reach extending substantially parallel to and overlying said sheet support means, with a portion of said member adjacent the upstream end of said reach converging toward said sheet support means to provide a sheet catching nip therebetween, said reach being movable at substantially the same speed as said sheet support means, and

straightening means for removing a curl from the leading edge of a sheet carried by said support means including an elongate, endless, flexible uncurling member, means training said uncurling member to provide an elongate reach thereof extending generally in the direction of said path, with said reach extending in an upstream direction from the upstream end of said hold-down reach and inclined outwardly and away from said support surface on progressing in said upstream direction, with an upstream portion of said reach spaced a distance outwardly from said support surface and remainder portions of said reach extending to a region adjacent said sheet catching nip and converging toward said support surface on progressing in a downstream direction relative to said path, and drive means for driving said reach at a speed faster than the speed of movement of said support means.

18. The apparatus of claim 17, wherein said holddown means comprises drive means for driving said reach of the hold-down member in the direction of said path at substantially the same speed as said support means is moved, and said uncurling reach is operatively connected to said drive means through means operable to drive said uncurling reach at a speed which is a preselected multiple of the speed of said hold-down reach. l= 

1. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprising an elongate, endless, flexible hold-down member, a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said hold-down member being trained around said training members to provide an elongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member being positioned to contact the face of a sheet opposite its face supported by said support means, means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said training members toward said support means, and means for driving said reach of the hold-down member in said one direction including a rotatable drive member over which said hold-down member is trained, which drive member is disposed between said pair of training members and is spaced outwardly from said reach of the hold-down member in a direction away from said path.
 2. The device of claim 1, wherein said drive means comprises an elongate, power-driven rotatable shaft spaced outwardly from and extending transversely of said path, said drive member is secured on said shaft for rotation therewith, and said means mounting a training member comprises an elongate support extending generally in the direction of said path pivotally mounted adjacent one of its ends on said shaft for swinging movement independent of rotation of said shaft toward and away from said support means and said training member is journaled on said support adjacent its opposite end.
 3. The device of claim 1, wherein said means mounting said training members comprises a first elongate support pivotally mounted adjacent one of its ends adjacent said drive member and extending in a generally downstream direction therefrom relative to said path with one of said training members journaled on said first support adjacent its other end, and a second elongate support pivotally mounted adjacent one of its ends adjacent said drive member and extending in a generally upstream direction therefrom relative to said path with the other of said training members journaled on said second support adjacent its opposite end, said first and second supports being swingable toward and away from said support means independently of each other.
 4. The device of claim 3, wherein one of said supports comprises means mounting its associated training member for shifting toward and away from the other of said training members generally in the direction of said path and means yieldably biasing said training member away from said other training member to maintain tension in said reach of the hold-down member.
 5. The device of claim 1, wherein said hold-down member comprises an elongaTe, flexible band having a substantially circular cross section, and one of said training members comprises a sheave having a width which is at least three times the diameter of said band and wherein the difference between the minor radius and the major radius of the sheave is less than the diameter of said band.
 6. The device of claim 5, wherein the opposite ends of said sheave have substantially the same diameter, the minor diameter of the sheave is disposed substantially centrally of said outer ends, and the surfaces of the sheave extending from said outer ends toward said minor diameter region are inclined at a substantially constant shallow angle relative to the rotational axis of the sheave.
 7. The device of claim 6, wherein said sheave has a shallow groove extending circumferentially thereabout in said minor diameter region.
 8. A sheet hold-down device for use with conveying apparatus including a support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprising, an elongate, endless, flexible hold-down member, a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said hold-down member being trained around said training members to provide an elongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member being positioned to contact the face of a sheet opposite its face supported by said support means, means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said training members toward said support means, means for driving said reach of the hold-down member in said one direction, and a deflector mounted intermediate said training members and closely adjacent the training member which is positioned farthest downstream in said apparatus relative to the direction of movement of said path, said deflector having a notch in its side facing toward the sheet support means adapted to receive and permit travel of a portion of said hold-down member thereunder.
 9. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprising, an elongate, endless, flexible hold-down band, a pair of training sheaves journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said hold-down band being trained about said training sheaves to provide an elongate reach extending in said direction adjacent and substantially parallel to said support, said reach of the hold-down band being positioned to contact the face of a sheet opposite its face supported by said support means, means mounting said training sheaves for shifting toward and away from said support means independently of each other and yieldably biasing said training sheaves toward said support means, reversible drive means for driving said reach of the hold-down band in said one direction or in a direction opposite said one direction, and a band guide pivotally mounted above said reach of the band intermediate said sheaves and closely adjacent said sheave toward which said reach of the band moves on being driven in said opposite direction, said guide having depending, laterally spaced, side portions extending downwardly on opposite sides of said reach of the band defining a guide channel therebetween which is substantially aligned with a band-receiving peripheral groove of the sheave near which it is mounted.
 10. The device of claim 9, wherein said guide is mounted for swinging upwardly and away from said band when the band is driven in said one direction and is reTained in a guiding position with its depending side portions guiding movement of said reach when said reach is moved in said opposite direction.
 11. A sheet hold-down device for use with conveying apparatus including support means for supporting one face of a sheet as it is moved along a path in the direction of one of its edges, said hold-down device comprising, an elongate, endless, flexible hold-down member, a pair of training members journaled for rotation about substantially parallel axes extending transversely of said path and spaced from each other in the direction of movement for a sheet, said hold-down member being trained around said training members to provide an elongate reach extending in said direction, adjacent and substantially parallel to said support, said reach of the hold-down member being positioned to contact the face of a sheet opposite its face supported by said support means, with the training member of said pair which is positioned farthest upstream relative to said path training said hold-down member in a bend whereby a sheet catching nip is defined between the hold-down member and the support means, means mounting said training members for shifting toward and away from said support means independently of each other and yieldably biasing said line-training members toward said support means, means for driving said reach of the hold-down member in said one direction, and straightening means for removing a curl from the leading edge of a sheet prior to such leading edge reaching said sheet catching nip, said straightening means comprising an elongate, endless, flexible uncurling member, means training said uncurling member thereover to provide an elongate uncurling reach for the uncurling member extending in a generally upstream direction relative to said path from a region adjacent said nip, with said uncurling reach diverging from said support means on progressing in said upstream direction, and means for driving said uncurling reach in the direction of said path at a speed faster than the speed at which a sheet is carried along said path.
 12. The device of claim 11, wherein the speed at which said hold-down member is driven corresponds to the speed at which a sheet is carried along said path by the conveyor, and which further comprises means operatively interconnecting said hold down means and said straightening means operable to drive said uncurling member at a speed which is preselected multiple of the speed of said hold-down member regardless of variations in the speed of the hold-down member.
 13. The device of claim 11, wherein said training means for said uncurling member comprises a wheel around which said uncurling member is trained, said wheel being journaled adjacent the upstream training member for the hold-down member and being so positioned that the portion of the uncurling member nearest said support means is spaced from said support means a distance greater than is said hold-down member at the nip between the hold-down member and the support means.
 14. Sheet-conveying apparatus for conveying a sheet along a path in the direction of one of its edges wherein the leading edge of such a sheet may be curled when supplied to the apparatus, comprising sheet-support means having a support surface for supporting one face of a sheet, and being movable at a first speed in the direction of said path to carry a sheet therealong, hold-down means including a power-driven, elongate hold-down member having an elongate reach extending substantially parallel to and overlying said sheet support means, with a portion of said member adjacent the upstream end of said reach converging toward said sheet support means to provide a sheet catching nip therebetween, said reach being movable at substantially the same speed as said sheet support means, and straightening means for removing a curl from the leading edge of a sheet carried by said support means including an elongate, endless, flexible uncurling member, meanS training said uncurling member to provide an elongate uncurling reach thereof extending generally in the direction of said path, with an upstream portion of said uncurling reach being spaced a distance upstream along said path from said sheet catching nip and spaced a distance outwardly from said support surface and with remainder portions of said uncurling reach extending from said upstream portion to a region adjacent said sheet catching nip and converging toward said support surface on progressing in a downstream direction relative to said path, and drive means for driving said uncurling reach at a speed faster than the speed of movement of said support means.
 15. The apparatus of claim 14, wherein said flexible uncurling member is an endless band and said training means comprises a pair of sheaves journaled for rotation about substantially parallel axes extending transversely of said path, with the sheave which is positioned downstream in said pair relative to said path being mounted with its peripheral edge nearer to said support means than the other of said sheaves.
 16. The apparatus of claim 14, wherein said sheet support means comprises variable speed drive means operable to move the sheet support means at selected speeds, and said uncurling means is operatively connected thereto through means operable to drive said uncurling reach at a speed which is a preselected multiple of the speed of the sheet support regardless of the speed of the support means.
 17. Sheet-conveying apparatus for conveying a sheet along a path in the direction of one of its edges wherein the leading edge of such a sheet may be curled when supplied to the apparatus, comprising sheet-support means having a support surface for supporting one face of a sheet, and being movable at a first speed in the direction of said path to carry a sheet therealong, hold-down means including a power-driven, elongate, endless, flexible band, and means training said band in a hold-down reach extending substantially parallel to and overlying said sheet support means, with a portion of said member adjacent the upstream end of said reach converging toward said sheet support means to provide a sheet catching nip therebetween, said reach being movable at substantially the same speed as said sheet support means, and straightening means for removing a curl from the leading edge of a sheet carried by said support means including an elongate, endless, flexible uncurling member, means training said uncurling member to provide an elongate reach thereof extending generally in the direction of said path, with said reach extending in an upstream direction from the upstream end of said hold-down reach and inclined outwardly and away from said support surface on progressing in said upstream direction, with an upstream portion of said reach spaced a distance outwardly from said support surface and remainder portions of said reach extending to a region adjacent said sheet catching nip and converging toward said support surface on progressing in a downstream direction relative to said path, and drive means for driving said reach at a speed faster than the speed of movement of said support means.
 18. The apparatus of claim 17, wherein said hold-down means comprises drive means for driving said reach of the hold-down member in the direction of said path at substantially the same speed as said support means is moved, and said uncurling reach is operatively connected to said drive means through means operable to drive said uncurling reach at a speed which is a preselected multiple of the speed of said hold-down reach. 